The following description provides a summary of information relevant to the present invention and is not an indication that any of the information provided or publications referenced herein is prior art to the presently claimed invention.
The electrokinetic separation of most analytes by electrophoresis is typically performed using buffers with wide range of pH (pH 3-10). Analytes such as peptides and proteins are positively charged under these buffer conditions. A popular and efficient way of performing electrokinetic separation on multiple samples is by capillary gel electrophoresis. Capillary gel electrophoresis systems typically employ fused silica capillary tubes. The surface of these fused silica capillary tubes is negatively charged above pH 2.0 because the silanol groups on the capillary surface become ionized. Consequently, the positively charged proteins and peptides traveling through the capillary during electrophoresis interact with the surface of the fused silica capillary and adsorb to the inner surface of the capillary tube. This is a problem because the adsorption of analytes continuously changes the surface properties of the capillary tube, resulting in changes in the electrosmotic flow velocity of the solution in the capillary. This causes a fluctuation of migration time of analytes which results in inaccuracies and poor reproducibility.
Attempts have been made to mitigate the adsorption of positively charged analytes to negatively charged fused silica capillaries. For example, capillary electrophoresis has been performed using running buffers with pH 2-4 to reduce the ionization of surface silanol groups. This approach can reduce the adsorption of analytes to a limited extent, but results in a reduction in sample throughput through the capillary and consequently longer run times. Also, attempts have been made to cover the capillary inner surface with neutral coatings. This approach also results in a reduction in sample throughput through the capillary. Capillary tubes having a positive coating have also been made, where monomeric amine silanes are covalently bonded to the capillary surface. A problem with these coatings is that they are unstable under acidic and basic conditions. None of the approaches used thus far have been ideal. What is needed are capillary tubes that are coated to obtain a longer run life, that can typically be used one hundred or more analysis with reproducible results, and that can be prepared by a fast and simple process. Also needed are capillary tubes and a capillary electrophoresis system that is useful for high-throughput analysis of proteins, peptides, and other analytes that adhere to capillary tubes during electrophoresis.